The present invention relates to tire building drums for laying up tire carcasses, more particularly to drums which are expandable between a collapsed position and an expanded position. The invention also relates to methods and apparatus for setting beads on green tire carcasses.
It is known that in making vehicle tires, for example for automobiles, that manufacture of a so-called carcass is first achieved by successively assembling several different components. In other words, the different carcass types included in a production range can be distinguished from one another depending on the presence thereon of the various accessory components and/or the typology of the accessory components themselves.
By way of example, when carcasses for tubeless tires are to be produced, that is tires that in use do not require the presence of an inner tube, the main components can be considered to include a so-called inner liner that is a layer of elastomeric air-impervious material, a carcass ply, a pair of annular metal elements, commonly referred to as bead cores, around which the opposite ends of the carcass ply are folded, as well as a pair of sidewalls made of elastomeric material, extending over the carcass ply at laterally opposite positions. The accessory components may in turn comprise of one or more additional carcass plies, one or more reinforcing bands for overlying the carcass ply or plies at the areas turned up around the bead cores (chafer strips), and others.
It is well known that the components of most pneumatic tire constructions must be assembled in a way which promotes good tire uniformity in order to provide proper tire performance. For example, a tread which xe2x80x9csnakesxe2x80x9d as it goes around the tire circumference will cause wobbling as the tire is operated. For example, a carcass ply which is lopsided (longer cords on one side of the tire than the other side) can cause a variety of tire nonuniformity problems including static imbalance and radial force variations. For example, a tire which is not meridionally symmetric (e.g., tread not centered between beads) can cause a variety of tire nonuniformity problems including couple imbalance, lateral force variations, and conicity. Therefore, in order to meet typical tire performance requirements, the tire industry generally expends considerable effort in producing tires with good uniformity. Tire uniformity is generally considered to mean tire dimensions and mass distributions which are uniform and symmetric radially, laterally, circumferentially, and meridionally, thereby producing acceptable results for measurements of tire uniformity including static and dynamic balance, and also including radial force variation, lateral force variation, and tangential force variation as measured on tire uniformity machines which run the tire under load on a road wheel.
Although certain degrees of tire nonuniformity can be corrected in post-assembly manufacturing (e.g., by grinding), and/or in use (e.g., applying balance weights to the rim of a tire/wheel assembly), it is preferable (and generally more efficient) to build-in tire uniformity as much as possible.
Typical tire building machines comprise a tire building drum around which the tire components are wrapped in successive layers including, for example, an innerliner, one or more carcass plies, optional sidewall stiffeners and bead area inserts (e.g., apex), sidewalls and bead wire rings (beads). After this layering, the carcass ply ends are wrapped around the beads, the tires are blown up into a toroidal shape, and the tread/belt package is applied.
Commonly-owned U.S. Pat. No. 5,591,288 (hereinafter referred to as xe2x80x9cBeckerxe2x80x9d) discloses mechanical tire building drums for building extended mobility pneumatic tires, and more specifically to a tire building drum having contours or depressions in its surface to facilitate building certain tire designs. Attention is also directed to corresponding published European Patent Application No. 0 634 266 A2.
As noted by Becker, tire performance can be affected by adding components to the tire or by adjusting the location of tire components in the tire during the tire building process. During the tire building process, it is important that components fit together well with a minimum of wrinkling of the tire components or trapping of air between the components. If air is trapped between the uncured tire components, the tire may be defective and may have to be scrapped. During the tire building process, if it appears the air has been trapped between tire components, the tire builder must stitch the interfaces between the uncured elastomeric components to work any bubbles or trapped air from between the components. This stitching involves rolling a roller wheel along the components, forcing the air to an edge of a component where it can escape. The stitching process is time consuming and requires the skill of the tire builder.
As further noted by Becker, this problem is further magnified in tire designs where components are rather thick compared to other components. For example, when a component having a relatively square cross-section, such as a tire bead, is positioned adjacent a more planar component, such as a ply, the air may be trapped where the different-shaped components interface. In tire designs where different-shaped components are necessarily placed next to each other, the problem of trapped air is even more difficult.
As further noted by Becker, in one particular extended mobility tire design, inserts are positioned in the sidewall between the carcass plies to enable the tire to support the weight of the vehicle even if the tire should lose inflation pressure. These inserts are typically thicker than the plies which lie adjacent to them and it is important that this tire be built without trapping air between the plies and inserts. In accordance with the present invention, an inventive tire building method and drum have been designed which have features to accommodate the special production needs of such tires. These special features will be described hereinafter and contribute to the building of a quality tire without trapping air.
Becker therefore provides a method of building a tire comprising the steps of forming a liner into a cylinder, positioning first inserts to indent the liner cylindrical surface circumferentially at axially spaced insert locations along the axis of the cylinder, laying a first ply of reinforcing material around the cylindrical surface of the liner and first insert, positioning second inserts over the first ply at the spaced insert locations, laying a second ply of reinforcing material over the first ply and the second inserts, positioning circular beads at each end of the cylinder, expanding the first ply and the second ply to increase the diameter of the cylinder between the circular beads to provide shoulders at each end of the cylinder, turning edges of the first ply around the second ply over each of the beads, and positioning a belt and tread assembly around the second ply to form a precured tire.
Becker further provides a method of assembling tire components on a tire building drum having a cylindrical surface comprising the steps of laying a liner on the surface of the drum, positioning first inserts below the cylindrical surface and around a drum at insert locations spaced from each end of the drum, laying a first ply of reinforcing material around the drum over the cylindrical surface of the liner and first insert, positioning second inserts over the first ply at the insert locations spaced from each end of the drum, laying a second ply of reinforcing material over the first ply and the second inserts, positioning circular beads at each end of the drum, expanding the drum to increase the diameter of the cylindrical surface and provide shoulders at each end of the drum, turning edges of the first ply and the second ply over each of the beads, positioning a belt and tread assembly around the second ply, and contracting the drum for removal of the assembled tire components from the drum.
Becker further provides a tire building drum which has a cylindrical surface, circular grooves in the surface at insert locations spaced from each end of the drum for positioning of first inserts below the surface, means for applying a first ply over the cylindrical surface, means for applying second inserts over the first ply and the first inserts, means for applying a second ply over the first ply and second insert, means for expanding the drum providing shoulders at each end of the drum for applying bead rings, means for turning up ends of the first ply around the beads, means for applying a belt and tread assembly around the second ply and means for contracting the drum to remove the assembled tire from the drum.
Commonly-owned U.S. Pat. No. 4,855,008 discloses an expandable tire building drum, especially a first stage solid pocket drum for building a carcass of a radial tire, having a segmental drum (10) with a plurality of axially-extending, circumferentially spaced segments (36) with flexible connections (56) to shoulder pistons (32) at opposite ends of each segment (36). Wedge shaped bars (62) are positioned between the segments (36) and are connected to center pistons (64) for urging tapered side faces (80) of the bars into engagement with sloping side faces (78) of the segments (36). The shoulder pistons (32) and center pistons (64) move radially outward to expand the drum. During the first stage operation, the tire reinforcing plies, beads and other components are assembled on the first stage drum and then the carcass is moved to another location where it is shaped and the belt and tread applied. In the first stage assembly of the tire carcass it is important that the tire components be applied to contracted and expanded drum surfaces which are concentric and of uniform diameter along the length of the drum. Expandible drums of different constructions have been used heretofore; however it has been difficult to maintain a concentric drum surface and a uniform diameter along the length of the drum in both the expanded and contracted condition of the drum. For example, the drum surface may be concentric and uniform in the contracted condition but is distorted during expansion to a larger diameter. As a result, the components added to the carcass on the expanded drum are not precisely assembled which may adversely affect the uniformity of the tire.
U.S. Pat. No. 5,264,068 discloses an expandable drum including adjustable stops for setting drum circumference. Tapering structures, each having axial slidability, are provided, and in response to a slide move of the tapering structure, drum segments are each radially expanded or retracted. As noted therein, the tapering structure (12) is of an inner recessed frustum and is mounted over the drum shaft (10) longitudinally or axially slidable with the aid of a key (16), and housed in the drum (14). The drum (14) is circumferentially divided into a plurality of drum segments (17), each being like a sector, and each segment (17) is interiorly supported by a drum segment supporter (18).
Commonly-owned U.S. Pat. No. 4,976,804 discloses an expandable, segmental tire building drum (1) having a plurality of circumferentially spaced drum segments (28) radially movable by a set of links (36) pivotally connected to a pair of axially movable hub assemblies (34) slidably mounted on a drum shaft (12). Each of the segments (28) has a cylindrical center portion (30) and end portions (32) with recesses providing pockets (68) for the tire bead portions. The links (36) are positioned between the end portions (32) providing space for large bead portions in the pockets (68) and at the same time the segments (28) are retractable to a small diameter to facilitate placing of a tire band (64) over the drum (10).
Commonly-owned U.S. Pat. No. 4,929,298 discloses a tire building drum including an expandable segmental cylinder assembly and a vacuum Chamber. The drum (10) has a plurality of axially-extending, circumferentially spaced segments (18). The ends of the drum are sealed to provide a vacuum chamber (76) inside the drum which is in communication with vacuum holes (78) in a cover sleeve (48) to hold tire components on the drum surface (58) during assembly of the tire components.
According to the invention, a tire building drum has a center section and two end sections. Each end section is provided with an expandable bead lock assembly. The center section is preferably expandable. The expandable bead lock assembly comprises a carrier ring and a plurality of elongate links extending between the carrier ring and a plurality of radially-expandable segments. When the carrier ring moves inward (towards the center section), the radially-expandable segments move radially outward, urging a plurality of axially extending, circumferentially spaced-apart finger segments outward from a collapsed position to an expanded position, and at least one position therebetween.
In an embodiment of the invention, the bead lock assembly comprises a cylinder and two pistons disposed within the cylinder. The pistons are free to move axially within the cylinder, in response to pneumatic pressure. The first piston is constrained from moving axially inward by rods. The second piston is connected by rods to the carrier ring. Pressurized air supplied through air lines and passageways in the cylinder control the movement of the pistons so that the beach lock assembly can be partially-expanded, fully-expanded, and retracted.
The bead lock assembly of the present invention works well in combination with a tire building drum having an expandable center section. As described herein, a tire building drum has alternating fixed and expanding segments in a center section of the drum. The expanding segments are axially-extending and circumferentially spaced-apart from one another, and their end portions are contoured (have recesses, or grooves) to accommodate tire components such as sidewall inserts. Two different mechanisms for expanding the center section are described. A first mechanism includes two wedge elements which are axially moveable away from one another to expand the center section. Ramp elements associated with the expanding segments may thus be moved radially outward. Biasing elements provide a restoring force for collapsing the center section. A second mechanism includes two guide rings which are axially moveable towards one another for expanding the center section, and away from one another to collapse the center section. Overlapping links are provided between the guide rings and a base member supporting the expanding segments.
According to the invention, there is disclosed a process of building a tire on a tire building drum having an expandable center section and two expandable end sections. The process includes the following steps of first applying an innerliner on a flat application surface of the tire building drum while the center section and the end sections are in their collapsed conditions. Then the center section and the end sections are expanded to an intermediate expanded condition to form a pair of spaced recesses on the center section of the drum. Next, a pillar insert is applied into each recess of the center section whereby the application surface across the building drum is substantially flat. Continuing, a first ply is applied onto the substantially flat application surface, followed by applying post inserts atop the first ply and substantially above the pillar insert, followed by applying a second ply. Then a pair of beads are moved into place above fingers of a bead lock assembly in each of the expandable end sections. Then, each bead lock assembly and the center section are expanded to their fully-expanded positions so that the fingers grip the inextensible beads. Next, the innerliner, first ply and second ply are turned up about the beads. Continuing, the bead lock assemblies and the center section are collapsed to their collapsed, unexpanded position. Finally, the tire is removed from the drum and the process starts again.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.